A dynamic mechanism for allosteric activation of Aurora kinase A by activation loop phosphorylation

Many eukaryotic protein kinases are activated by phosphorylation on a specific conserved residue in the regulatory activation loop, a post-translational modification thought to stabilize the active DFG-In state of the catalytic domain. Here we use a battery of spectroscopic methods that track different catalytic elements of the kinase domain to show that the ~100-fold activation of the mitotic kinase Aurora A (AurA) by phosphorylation occurs without a population shift to the DFG-In state, and that the activation loop of the activated kinase remains highly dynamic. Instead, molecular dynamics simulations and electron paramagnetic resonance experiments show that phosphorylation profoundly alters the structure and dynamics of the DFG-In subpopulation, leading to activation of the kinase. Kinetics experiments tracking structural transitions during nucleotide binding suggest that a substantial DFG-Out subpopulation is an important feature of activated AurA that evolved to optimize the kinetics of substrate binding and product release.